Several methods are currently used to determine the height of ink in the ink supply reservoirs in printers such as solid ink jet printers. The word “printer” as used herein encompasses any apparatus, such as digital copier, bookmaking machine, facsimile machine, multi-function machine, etc. which performs a print outputting function for any purpose. Examples of the methods include: (1) conductive level sense probe; (2) over-driven thermistor; and (3) vibrating beam.
The conductive level sense probe involves a single-point method of determining if the reservoir is full. When the height of the ink rises to a level touching the probe, an electrical current can pass from the probe through the ink to ground, thereby registering that the ink is at the height of the probe tip.
The over-driven thermistor also involves a single-point method of determining ink height. When the thermistor is covered by ink, the thermistor is quenched to a lower temperature. This causes the thermistor to send a different resistance reading to a controller indicating that the ink is at the height of the thermistor.
The vibrating beam or “twanger” is a form of continuous ink level sensing. The resonance of the beam changes as a function of the amount of the beam immersed in ink (i.e., the ink level).